The subject matter disclosed herein relates generally to light curtains and, more specifically, to safety light curtains for monitoring a protective field and to such light curtains which comprise optoelectronic components interconnected by a communication bus. Furthermore, the present invention relates to optical units which are part of such a light curtain and to a method for allocating individual addresses to each of a plurality of optoelectronic components.
Generally, light curtains and in particular safety light curtains detect the movement or intrusion of objects into guarded zones, and more particularly, provide protection for human operators who are working with machines or other industrial equipment.
Light curtains employing infrared or visible light beams are used to provide operator safety in a variety of industrial applications. Light curtains typically are employed for operator protection around machinery, such as punch presses, brakes, molding machines, automatic assembly equipment coil winding machinery, robot operation, casting operations and the like. Conventional light curtains typically employ light emitting diodes (LED) mounted at spaced positions along a transmitter bar at one side of the guard zone and phototransistors (PT), photodiodes or photoreceivers mounted along a receiver bar at the opposite side of the zone. The LEDs transmit modulated infrared light beams along separate parallel channels to the PTs at the receiver bar. If one or more beams are blocked from penetration by an opaque object, such as the operator's arm, a control circuit shuts the machine down, prevents the machine from cycling, or otherwise safeguards the area.
Usually, safety light curtains comprise two optical units (also called bars, sticks, edges or strips), which are formed as two different constructional units, one of the optical units having the functionality of an emitter and one of a receiver. This dedicated architecture of an emitter and receiver, however, has several drawbacks.
Firstly, the fabrication costs are high, because each type of optical unit has to be fabricated differently. Further, it is known to use the optical path from the emitter to the receiver also for transmitting information, for instance for a synchronization. However, in a system where one of the optical units has only the function of an emitter and the other one only the function of a receiver, the optical communication is only unidirectional, i.e. from the sender side to the receiver side. Therefore the optical synchronization may be difficult and a transmission of communication information is possible only in one direction.
It has already been proposed to locate receivers and transmitters on each of the first and second optical units, as this is described in the European patent EP 1870734 B1. Here, the grid has two identical transmitting/receiving strips, to which transmitting and receiving units are fixed. The transmitting/receiving strips are placed opposite to each other with a protective field being formed between the strips. The transmitting/receiving strips are identically formed in control and evaluation units. The control and evaluation units have safety outputs, which are formed together as a switching channel. An identical power supply is provided for all the strips.
Furthermore, it is known from EP 2511737 A1 to provide a modular light curtain and optical unit for such a light curtain.
Whenever electronic components are interconnected by means of communication bus, it is necessary that each of the components has a clearly distinguishable individual address which is also known to the controller for providing data intended for the particular electronic component in the downlink and for distinguishing between the data sent by a particular component in the uplink. When assembling light curtains containing a plurality of optoelectronic components each may be provided with a particular address which is stored in the controller and the optoelectronic component itself, so that the communication can take place. The address value is normally pre-defined and correlated with a particular function within the bus system and such a pre-defined address allocation has the disadvantage that this particular function of a component within the bus has to be known before assembly. In the case of light curtains having optoelectronic components with sender and/or receiver elements this means that during assembly each optoelectronic component has to be mounted in a pre-defined assembly location corresponding to its address.
Thus, it would be desirable to provide a light curtain and a method for allocating an individual address to each of a plurality of optoelectronic components, which reduces the expenditure during assembly and also complies with the requirements for a design for testability and maintenance.